Physical Geography of Louisiana USA Term Paper

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Topography of Louisiana

Louisiana encompasses an area of 51,844 square miles, and is the 31st largest state. The elevations of Louisiana range from 8 ft below sea level at New Orleans to a maximum of 535 ft at Driskill Mt, with a mean elevation of 100-ft (Buchanan, W.C., 1957, pp1-6). Along the Gulf of Mexico, Louisiana's coastline is 397 miles long. All of Louisiana lies within the Gulf Coastal Plain. There are three subregions of the Gulf Coastal Plain; the East Gulf Coastal Plain, the West Gulf Coastal Plain, and the Mississippi Alluvial Plane. The Florida Parishes are a part of the East Gulf Coastal Plain, and western Louisiana is a part of the West Gulf Coastal Plain. The Mississippi Alluvial Plain separates the East and West Plains. Louisiana has a number of geographic regions, which are defined on the basis of climate, soil, relief, and vegetation (Buchanan, 1957, pp1-6). These regions are termed (1) coastal marshes, (2) the Mississippi floodplain, (3) the Red River valley, (4) terraces, and (5) hills.

The coastal marshes represent the transition zone between land and ocean. Both elevation and relief are low in the coastal marshes however cheniers and salt domes rise above the low surfaces. Both freshwater and saltwater marshes exist in the coastal wetlands.

The Mississippi floodplain dominates the North-South alignment of Louisiana. The Mississippi floodplain is divided into (1) the passes, (2) natural levees, and (3) swamps. The passes (delta) have specific features that include mudlumps and bars. Natural levees are riverbanks built up over time by flood-deposited sediments and stand above the surrounding floodplains. Swamps occupy low-lying areas such as the Tensas Basin and the Atchafalaya Basin.

1. The terraces region comprises those ancient structures formed by the ice age Mississippi along the flanks of the present floodplain. Three sub-regions comprise the terraces: (1) the blufflands, (2) the flatwoods, and (3) the prairies. The blufflands have the highest relief and more vertical slopes. Both the flatwoods and the prairies have lower relief, and can be distinguished based on the vegetation. The flatwoods are characterized by longleaf pine forest, whereas the prairies are characterized by grasslands (Kniffen and Hilliard, 1968, pp 11-16).

The hill country of western and north central Louisiana and the Florida Parishes represents the highest elevations in the state. These hills are associated with layers of rock, which have been folded upward. In the Florida Parishes the hill country results from an upwarping (rock strata upwardly bending along a line) known as the Wiggins Anticline (Buchanan, 1957, pp1-6). Vertical bluffs form in the hilly area, which create a steeper terrain. In this area, relief is at its greatest, and the hills and valleys support a forest of mixed pine and hardwoods.

The land throughout Louisiana is extremely rich in mineral resources, of which petroleum and natural gas are by far the most important (U.S. Geologic Survey, State of Louisiana, 1968). Major oil fields are located in the southern portions of the state, offshore in the Gulf of Mexico, and in the northwest region. Significant salt and sulfur deposits are found throughout the coastal marsh region, as are commercial quantities of sand, stone, and clay important (U.S. Geologic Survey, State of Louisiana, 1968).

Louisiana has a number of rivers and streams that traverse the state. At least twenty-nine streams are classed as navigable by the U.S. Army Corps of Engineers. The Mississippi River and its major tributaries, which include the Red, Ouachita, and Atchafalaya rivers, have deposited so much material that their beds are now higher than much of the surrounding land. Natural flood-control drainage takes place within a series of bayous (swampy outlets of rivers). The Black, Pearl, and Sabine rivers are also important to the state's drainage system. Lake Pontchartrain is the state's largest inland water body. Oxbow lakes (freshwater lakes occupying old river channels) are found along the Mississippi River and its tributaries.

Natural lakes are also scattered throughout the state (Louisiana Almanac, 1992-1993)

The Mississippi River dominates not only the state but also the continent, with a drainage basin touching thirty-one states and two Canadian provinces and encompassing over 1,245,000 square miles. From the Arkansas boundary to the Gulf the river flows some 569 miles, but with an average gradient of only two and one-half inches per mile. Within Louisiana the river is widest in East Carroll Parish (7,600 feet) and narrowest at Irvine Light near Bayou Sara in West Feliciana Parish (1,700 feet). Efforts have been made to stabilize the river in its present course by means of levees and artificial floodways through which excess water is diverted. Other river systems drain various parts of the states. The second largest river in Louisiana is the Red River. The Red River's headwaters are in New Mexico, and the river enters Louisiana in the northwest corner. The river then flows southeastward to its confluence with the Atchafalaya and Mississippi. Tributaries to the Red include Bayou Pierre, Bayou Dorcheat, Saline Bayou, Black Lake Bayou, and Little River. In the northeast the Ouachita-Black flows southward from Arkansas to the Red. The Ouachita-Black receives water from the Tensas River-Bayou Macon system, Boeuf River, Bayou D'Arbonne, Bayou de L'Outre, and Bayou Bartholomew. Southwest Louisiana is drained by two main systems -- the Sabine and the Calcasieu. The Sabine's headwaters are in north central Texas, and the river receives several small tributaries in Louisiana before flowing into the Gulf. The Sabine forms the Louisiana-Texas border for approximately three hundred miles. The Calcasieu, which lies entirely within Louisiana, flows first to the east then back to the west before emptying into Calcasieu Lake. Other major streams in the region are the Mermentau and Vermilion. The major south Louisiana streams are the Teche, Atchafalaya, and Lafourche, all of whose courses lie totally within the state. The Atchafalaya emerges from the junction of the Red and Mississippi, thence flows southward to the Gulf.

2. In the Florida Parishes several streams flow out from Mississippi generally southward to Lakes Maurepas, Pontchartrain, or Borgne. From west to east these streams include the Amite, Tickfaw, Tangipahoa, Tchefuncte, Bogue Chitto, and Pearl. The Intracoastal Waterway, a largely artificial watercourse, extends across Louisiana as part of a system that runs along the Atlantic and Gulf coasts. The 318-mile waterway provides an East-West route not provided by natural streams.

Various types of natural lakes exist. Cut-off or oxbow lakes (for example, False River, Bruin, Larto) form when a stream "cuts off" the neck of a meander (bend) to create a new course. Particularly along the valley of the Red, raft lakes (Caddo, Cross, Bistineau, Black, and others) were formed from waters dammed by the Great Raft, a logjam that clogged the river until it was finally removed. Lakes form along the coast when cheniers (beach ridges) act to slow the flow of rivers while also protecting the resulting lake from encroachment by the Gulf. Lakes Pontchartrain, Maurepas, and Catahoula exist in grabens, depressions in the earth bounded by faults. Other natural lakes are associated with the drainage in the vicinity of rivers, deltas, and salt domes

Louisiana has rich coastal and inland fishing waters, and although fishing accounts for less than 1% of the annual gross state product, the annual catch landed in Louisiana is greater than that of any other state except Alaska. More than three-quarters of the catch is menhaden. Shrimp is the second largest catch by volume but is first in value. Oysters and blue crabs are also significant (Newton, 1987)

The forestlands of Louisiana contain a variety of both softwoods and hardwoods. Commercial species include southern pine, oak, ash, cypress, gum, cottonwood, and willow. Except for the coastal marshes and the southwestern prairies, the state's original, natural vegetation consisted of mixed forests of evergreen and deciduous trees. The alluvial valleys had stands of cypress, oak, magnolia and other hardwoods intermixed with canebrakes. Oak, gum, magnolia, cottonwood, sycamore, cypress, tupelo, and other deciduous trees dominate the alluvial, bluff, and terrace lands. Individual species vary largely with elevation and relief. The uplands and part of the terraces are occupied by longleaf pine forests in some regions and in others by shortleaf or longleaf pine mixed to varying degrees with oak, hickory, and other hardwoods.

Louisiana has an abundance and diversity of plant and animal life. Commercial forests cover nearly half of the state's total area. Hardwoods, particularly oak, are mixed with shortleaf pine throughout the northwest. Cypress and oak forests, frequently covered by Spanish moss, thrive throughout the lowland south. Flowering plants, including azalea, magnolia, camellia, lily, and orchid, are also common. The present configuration of Louisiana's forests divides the state into five categories (Louisiana Almanac, 1992-1993, pp 97-103). About half of the total forest today are composed of hardwood species, and half of softwood species. Most of the softwood trees are loblolly pine and shortleaf pine. Loblolly-shortleaf pine forests dominates north central Louisiana, an areas west of the Red, and the middle of the Florida Parishes. A longleaf-slash pine forest is located largely in west…

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